BR102012032901B1 - METHOD TO SEEK AN UNDERGROUND HOLE, METHOD TO SEEK ANNULAR SPACE, METHOD TO ANALYZE ANNULAR SPACE AND METHOD TO MONITOR A FILLING WITH UNDERGROUND GRAVEL - Google Patents

Abstract

method for ascertaining an underground hole, method for ascertaining an annular space, method for analyzing an annular space and method for monitoring a filling with underground gravel. the present invention relates to the monitoring of scattered gamma rays and is used to identify substances arranged between coaxial tubes 412 arranged in an underground hole 402. the gamma rays are strategically directed from the inside of an inner tube 412 to the inside of the annular space 422 and some of the gamma rays disperse from the substance between the tube 412s and are detected with the detectors set at a designated axial distance from the gamma ray source 428. the gamma rays also disperse from the fluid in the inside tube 412, a ratio of the detected gamma rays that disperse from the fluid in tube 412 and from the substance can be used to determine the substance.

Description

“METHOD TO SEEK AN UNDERGROUND HOLE”

Field of the Invention

[001] The invention generally refers to the investigation of an annular space between the tubes arranged in an underground hole. More specifically, the present invention relates to a device and method that uses a radiation source to ascertain an underground annular space and a radiation detector to identify a substance or substances in the annular space.

Background of the Invention

[002] Underground holes used to produce hydrocarbons are typically aligned with a column of the compartment that is cemented in the cross formation by the hole. Often an inner housing column is inserted into the compartmental column cemented in place. The fluid produced from the well flows to the surface inside the production pipe, which is inserted inside the internal housing column. During the life of a typical well, production piping can be removed so that repair, repair, or flow enhancement operations can be initiated in the well. There may also be a need at some point to remove a portion or the entire compartment.

[003] Generally, drilling fluids fill the annular space between concentric tubes. Particulate matter inside the drilling fluids can settle or precipitate over time and form a cement-like substance that is coupled with the concentric tubes and prevents removal of the inner tube from the hole. Although cutting tools can cut the tubes to allow removal of the unobstructed portion, the tube cannot be removed if the cut is made at a depth below which the tubes are attached to each other.

Alternatively, a very shallow cut may leave a portion

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2/32 undesirably long free pipe that extends above the adhesion point.

Description of the Invention

[004] A method for ascertaining an underground hole is provided in this document. In one example the method includes generating radiation from the inside of a tube that is disposed in the underground hole. The radiation is directed along a path that is oblique to a geometric axis of the tube that allows part of the radiation to pass through the tube into an annular space that surrounds the tube and disperses back into the tube . A portion of the radiation that disperses back into the tube is detected and a count of the detected radiation is used to identify a material in the annular space. Alternatively, radiation is a first set of radiation and the path is a first path. In this example, the method additionally includes directing a second set of radiation along a second path that moves away from the first path. A part of the second set of radiation disperses from the fluid disposed in the tube and is detected. Thus, in an exemplary embodiment, identifying a material in the annular space is additionally based on a detection rate of the second set of radiation. The radiation can be a gamma ray from a gamma ray source that has an energy of about 250 keV to about 700 keV. In this example, scattered radiation when detected has an energy of about 50 keV to about 350 keV. In an alternative embodiment the method may also include detecting a substantially solid material in the annular space when a ratio of the detection rate of the first set of radiation above the detection rate of the second set of radiation remains substantially the same with changes in thickness. In one example, the material in the annular space is a lightweight cement.

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[005] Also included in this document is a method for ascertaining an annular space between the inner and outer tubes arranged in a coaxial manner that include providing a source of gamma ray against an azimuthal section of the inner tube. The method also includes directing the gamma rays from the source so that some of the gamma rays move into the annular space and disperse from a material in the annular space back into the inner tube. In this example, some of the gamma rays move away from the azimuth section and disperse from a fluid in the inner tube. Gamma rays that disperse back can be detected, the method can also include classifying by gamma energy the gamma rays that disperse from the fluid in the inner tube and disperse from the material in the annular space and identify the material in the annular space based on a detection rate of scattered gamma rays. In an alternative, a conically shaped guide is provided close to the gamma ray source and positioned so that a hole in the guide is directed towards the source and the guide has a geometric axis that is substantially parallel to a geometric axis of the inner tube. The detector can be arranged from about 5.08 cm (2 inches) to about 10.16 cm (4 inches) from the gamma ray source and where the detector is used to detect scattered gamma rays. In one example, a collimator is used to strategically direct the gamma rays away from the source at an oblique angle to a geometric axis of the inner tube and along distinct paths azimuthally arranged around the gamma ray source, so that strategically located detectors, respectively, detect dispersion from distinct azimuthal areas radially spaced out from the gamma ray source. Optionally, a rate of detection of gamma rays dispersed from the fluid in the bore is used as a reference to determine the material in the annular space. The steps to generate and detect

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4/32 can be repeated at different depths in one section of the hole. A substantially solid material in the annular space can be identified when a ratio of a rate of detected gamma rays that are dispersed from the annular space above a rate of detected gamma rays that are dispersed from the fluid in the inner tube, remains substantially at with changes in the thickness of the annular space. Optionally, a fluid can be identified in the annular space when a gamma ray rate detection ratio is reduced with a reduction in the thickness of the annular space.

[006] A method for analyzing an annular space between an inner tube and an outer tube that are coaxially arranged in an underground hole is provided in this document which includes providing a gamma ray source against an azimuthal section of the inner tube and directing the gamma rays from the source so that some of the gamma rays move through the side wall, into the annular space and disperse from a material in the annular space back into the inner tube and so that some of the gamma rays move away from the azimuth section and disperse from a fluid in the inner tube. In this example, scattered gamma rays are detected and dispersed from the fluid in the inner tube and dispersed from the material in the annular space and classified. The material in the annular space is identified based on a detection rate of the scattered gamma rays. The steps of this method can be repeated at different depths in a section of the hole and a substantially solid material identified in the annular space when a ratio of a rate of detected gamma rays that are dispersed from the annular space above a rate of detected gamma rays which are dispersed from the fluid in the inner tube remains substantially the same with changes in the thickness of the annular space. A material substantially

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5/32 liquid is identified in the annular space when a ratio of a rate of detected gamma rays that are dispersed from the annular space, above a rate of detected gamma rays that are dispersed from the fluid in the inner tube, is reduced with a reduction in the thickness of the annular space. In an alternative, the rate of detection of gamma rays that are dispersed from the fluid in the tube is a reference value for use in identifying a liquid in the annular space.

Brief Description of Drawings

[007] Some of the features and benefits of the present invention have been declared, others will become apparent as the description proceeds when taken in conjunction with the attached drawings, in which:

Figure 1 is a schematic of an exemplary embodiment of a downhole imaging tool that has a low energy radiation source and detectors arranged in a bore according to the present invention;

Figure 2 is a perspective view of an embodiment of the tool of Figure 1;

Figures 3A and 3B are sectional views of an exemplary embodiment of the tool in Figure 2;

Figure 4 is an example of a graph representing a source response in a gravel filling for the detection of baritin curvature;

Figure 5 is a graph of a counting rate versus depth measured by an exemplary embodiment of an imaging tool in accordance with the present invention;

Figure 6 is a side sectional view of an alternative exemplary embodiment of the tool of Figure 1 arranged in a coated hole according to the present invention;

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6/32 Figure 7 is a side sectional view of a portion of the Figure shown with additional details;

Figure 8A is a side sectional view of the tool and the hole of Figure 7;

Figure 8B is a side sectional view of the tool and the hole of Figure 8A;

Figure 9A is a side sectional view of the tool and the hole of Figure 7 with the production piping arranged asymmetrically within a compartment column;

Figure 9B is a side sectional view of the tool and the hole of Figure 9A;

Figure 10 is a graphical representation of changes in the thickness of the annular space between the concentric downhole tubes and the gamma ray count rates reflected from the materials in the annular space;

Figure 11 is a graphical representation of changes in the thickness of the annular space between the concentric downhole tubes and a measured response of the gamma rays deflected from the materials in the annular space;

Figure 12A is a partial sectional side view of an example of a hole imaging tool that obtains a baseline image of a gravel fill according to the present invention;

Figure 12B is a partial sectional side view of the tool of Figure 12A that images the filling with gravel at a time after that of Figure 12A according to the present invention;

Figure 12C is a partial sectional side view of an example of an imaging tool that images a filling with gravel

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7/32 after a gravel filling repair step according to the present invention;

Figure 13 is a partial sectional side view of an exemplary embodiment of an imaging tool that images a compartment connection according to the present invention;

Figure 14 is a partial sectional side view of an exemplary embodiment of an imaging tool that images asphaltenes in a gravel filling according to the present invention; and Figure 15 is a partial sectional side view of an alternative embodiment of the imaging tool of Figure 6 shown substantially centered in a hole.

[008] Although the invention is described in connection with the preferred embodiments, it will be understood that this description is not intended to limit the invention to realization. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.

Description of Realizations of the Invention

[009] The method and system of the present presentation will now be described more fully hereinafter with reference to the accompanying drawings in which the achievements are shown. The method and system of this presentation can be in many different forms and should not be construed as limited to the illustrated achievements set out in this document; on the contrary, these achievements are provided so that this presentation will be perfect and complete and will fully convey its scope to the technicians in the subject. Similar numbers refer to similar elements throughout the present

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8/32 document.

[010] It should be further understood that the scope of this presentation is not limited to the exact details of the construction, operation, exact materials, or achievements shown and described, the modifications and equivalents will be apparent to a person skilled in the art. In the drawings and in the descriptive report, there may be illustrative achievements presented and although specific terms are used, they can be used in a generic and descriptive sense only and not for the purpose of limitation. Consequently, the improvements described in this document should therefore be limited only by the scope of the appended claims.

[011] Referring now to Figure 1, a downhole imaging tool 100 is shown positioned in a base pipe or internal steel housing 110 of a gravel filling. It is recognized that a tool housing 130 can be constructed from any light metal where the term light metal, as used herein, refers to any metal that has an atomic number less than 23. The tool Downhole imaging 100 includes at least one housing or a pipe 130 carrying a low energy radiation source 120 and a plurality of detectors 140. In an exemplary embodiment, the gamma radiation source 120 is centrally located in housing 130. Optionally, detectors 140 are spaced symmetrically from each other azimuthally at a constant radius, but also positioned inside housing 130. In other words, in an example, the radius at which detectors 140 are spaced from each other is less than than the radius of the housing 130. The radiation source 120 emits radiation, in this case, gamma rays 124 in the filling with gravel 150.

[012] The alternate hatch of the gravel filler 150

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9/32 indicates possible gravel filling regions that could be filled with gravel or not. For example, the central region 151 can constitute a vacuum in the gravel filling 150 that has been filled with finishing fluids or production fluids through which other regions 153 can constitute portions of the gravel filling that are completed or filled appropriately. Obviously, those skilled in the art, with the benefit of this presentation, will appreciate that the aforementioned regions are for illustrative purposes only and that a vacuum or bag can have any shape and any position in relation to tool 100.

[013] In the example in Figure 1, the gamma rays 124 that propagate into the filling with gravel 150 are dispersed by Compton (as in point 155), with loss of some energy, back towards the detectors 140 located in the indoor downhole imaging tool 100. Upon dispersion of gamma rays, they become gamma rays with lower energy 126, which are detected by detectors 140. The intensity of the count rate of the scattered gamma rays by Compton 126 depends among other factors, the density of the gravel filling material. So, higher count rates represent higher density in the gravel filling, where lower count rates represent a lower density as a result of less gamma rays that are dispersed back towards the detectors.

[014] In one example, radiation source 120 includes barium, cesium, some other low-energy radiation source, or combinations thereof. By using a low energy source such as this, the energy is propagated only a short distance into the gravel filling immediately adjacent to a screen. For this

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10/32 same reason, in one example, detectors 140 are positioned in housing 130 next to radiation source 120. In an exemplary embodiment, radiation source 120 and detectors 140 are within about 7.62 cm ( 3 inches) about 8.89 cm (3.5 inches) apart along tool length 100.

[015] The shield (not shown in Figure 1) can be applied around the radiation source 120 to collimate or otherwise limit the radiation emission from the radiation source 120 to a limited longitudinal segment of gravel fill 150 In one embodiment, such a shield is a heavy metal shield, such as sintered tungsten, that collimates the path for the gamma rays emitted into the interior of the gravel filling. Similarly, as described in more detail below, a similar shield can be used around each detector to limit the detector's viewing hole to only the gamma rays that are mainly singularly dispersed back to the detector from a specific azimuth section of the gravel filling.

[016] In addition, the energy levels of the emitted gamma rays 124 can be selected to assess the density of gravel filling at varying depths or distances from the downhole imaging tool 100. As an example, radiation from from a low energy gamma ray source, such as a 133Ba source, can be used to emit various energy levels. Alternatively, a source of gamma ray radiation with an energy close to 137 Cs can be used.

[017] Techniques for converting radiation count rates into a complete 2D profile map of the gravel filling integrity include the 3D curve method of the SYSTAT table. Other techniques include, but are not limited to, MATLAB, IMAGE, and advanced registration and techniques for making mosaic representations from data points

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11/32 can be used to map the base pipe and the gravel filling environment. Also, software based on 3D geostatistics can be adapted to convert the basic gamma ray counting rates to generate a map of the gravel filling environment. In this way, the integrity of a gravel fill or formation can be determined.

[018] To produce the precisely oriented maps, the azimuth angle of the profiling tool in relation to the elevated side of the well hole is determined. This orientation can be determined using any guidance device known in the art. The guidance devices may contain one or more orientation sensors used to determine the orientation of the profiling tool with respect to a reference plane. Examples of suitable guidance devices include, but are not limited to, guidance devices produced by MicroTesla of Houston, Tex. Each set of gamma ray measurements can be associated with such an orientation so that a 2D profile map of the gravel filling can be generated precisely in terms of the actual azimuth location of the material in the gravel filling.

[019] Figure 2 illustrates a perspective view of a gravel filling imaging tool. As shown, the downhole imaging tool 200 includes a housing 230 that carries radiation source 220, source collimator 225, and a plurality of radiation detectors 240 in an array. The detector array 240 can be positioned at a fixed distance from the radiation source 220. In certain embodiments, the detector array can be positioned at different distances from the radiation source 220. Additionally, the detector array in both the sides of the radiation source 220 are also provided for in certain embodiments. The

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12/32 electronic components 260 can also be located in housing 230 or wherever convenient.

[020] The radiation source 220 may be one or more radiation sources, which may include any suitable low-energy gamma-ray source capable of emitting gamma-ray radiation from about 250 keV to about 700 keV. The gamma ray source suitable for use with the embodiments of the present invention can include any suitable radioactive isotope that includes, but is not limited to, barium, cesium, LINAC radioactive isotopes, high energy x-rays (for example, about 200+ keV), or any combination thereof. The radiation from the radiation source 220 can be continuous, intermittent, periodic, or in certain embodiments, amplitude, frequency, modulated by phase, or any combination thereof.

[021] In an exemplary embodiment, the radiation source 220 is centrally located in housing 230. In the illustrated embodiment, source 220 is positioned along the geometric axis of housing 230.

[022] The gamma ray collimator 225, which is optional in certain embodiments, can be configured adjacent to source 220 in order to directionally restrict radiation from radiation source 220 to a segment of azimuthal radiation from the filling with gravel. For example, collimator 225 may include fins or walls 226 adjacent to source 220 to direct gamma ray propagation. Through directing, focusing or otherwise orienting the radiation from the radiation source 220, the radiation can be guided to a more specific region of the gravel filling. It is appreciated that in certain embodiments, a heavy metal closing mechanism could be employed additionally to direct the radiation from the radiation source 220. Additionally, the radiation energy can be selected,

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13/32 by choosing different isotopic sources, in order to provide some discrimination of lithological or spatial depth.

[023] In the illustrated embodiment, collimator 225 restricts radiation from source 220. In this embodiment, collimator 225 is also conically shaped as in 228, towards detectors 240 to collimate gamma rays from source 220. Obviously , those skilled in the art will appreciate that collimator 225 can be configured in any suitable geometry to direct, focus, guide or otherwise direct the radiation from the radiation source 220 to a more specific region of the gravel filling.

[024] In a non-limiting example, radiation transmitted from source 220 into a gravel fill (such as gravel 150 in Figure 1) is dispersed by Compton back from the gravel fill to tool 200 where the scattered radiation back can be measured by radiation detectors 240. Radiation detectors 240 can be any plurality of sensors suitable for detecting radiation, including gamma ray detectors. In the illustrated embodiment, four detectors are described, although several detectors can be used. In another exemplary embodiment, three detectors or six detectors are used; optionally, each detector is arranged to display a different segment of the gravel filling. With the use of multiple detectors, the tool can image the entire circumference of the gravel filling in separately identifiable segments. The resolution of the total circumference image may depend on several detectors, the gamma ray energy and the degrees of shielding provided around each detector.

[025] In certain embodiments, gamma ray detectors may include a sparkling crystal that emits light proportional to the energy

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14/32 deposited on the crystal by each gamma ray. A photomultiplier tube can be attached to the crystal to convert the light from the scintillation crystal to the measurable electron current or voltage pulse, which is then used to quantify the energy of each detected gamma ray. In other words, gamma rays are quantified, counted, and used to estimate the density of the gravel filling adjacent to the screen. Photomultiplier tubes can be replaced with a device coupled with a high temperature load (CCD) or microchannel photoamplifiers. Examples of suitable sparkling crystals that can be used include, but are not limited to, NaI, NaI (T1), BGO, and lanthanum-bromide crystals, or any combination thereof. In this way, counting rates can be measured from the radiation returned, in this case, the gamma rays returned. The intensity of the Compton scattered gamma rays depends on, among other factors, the density of the gravel filling material. Thus, the lower density represents the spans in the gravel filling and the lower count rates represent the lower density as a result of less gamma rays being dispersed back towards the detectors.

[026] In an exemplary embodiment, detectors 240 are mounted inside a housing within a radius smaller than the housing radius 230 inserted from the housing surface 230. Similarly, although they do not need to be spaced equally , in the illustrated embodiment, detectors 240 are equally spaced in the selected radius. Although the illustrated example shows four detectors 240 spaced 90 degrees apart, those skilled in the art will appreciate that several multiple detectors can be used in the invention. Furthermore, although the embodiment illustrates all detectors 240 positioned at the same distance from source 220, they do not need to be spaced equally. So, for example, a detector (or an array of multiple detectors) can

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15/32 be spaced 12 centimeters from the source, although another detector (or detector array) is spaced 20 centimeters from the source or any other distance inside the tool.

[027] Similarly, in another embodiment, detectors 240 can be positioned both above and below source 220. In such a case, collimator 225 would be appropriately shaped to guide the gamma rays towards the desired detectors. In such embodiments with multiple detectors disposed on both sides of the radiation source, additional shielding can be provided between the collimators to prevent radiation scattering (i.e., cross-contamination of radiation) from the segment other than filling with gravel.

[028] Each detector 240 can be mounted so as to be shielded from other detectors 240. Although any type of shielding configuration can be used for detectors 240, in the illustrated embodiment, collimator 248 is provided with a plurality of openings or slots 245 spaced apart around the perimeter of collimator 248. Although openings 245 can have any shape, such as round, oval, square or any other shape, in an exemplary embodiment, openings 245 are shaped like elongated slits and will be referred to as this document.

[029] A detector 240 is mounted in each slot 245, in order to enclose detector 240 in the shield. Slot 245 width and depth can be adjusted as desired to achieve the desired azimuth range. In certain embodiments, the length of the slits 245 can be as long as the sensitive region of the gamma ray detector (for example, the height of the crystal). It will be appreciated that since a detector is arranged inside the slot, the detector is not on the surface of the collimator where it could otherwise detect gamma rays from a range

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Greater azimuth 16/32. In an exemplary embodiment, slot 245 is 360 / (several detectors) degrees wide and the detector faces the inner diameter of the pressure housing which is a few millimeters deep (for example, from about 2 to about 5 mm). However, closer collimation is possible. Optionally, the azimuth range of each slot is limited to 360 / (multiple detectors) degrees. In this way, the view of each radiation detector 240 can be more focused on a particular region of the gravel filling. In addition, such shielding eliminates or at least smoothes the scattered radiation from one detector to another detector. As can be seen, each detector is separated from each other by the radiation-absorbing material. By eliminating more accurate azimuth readings of the radiation dispersion from detector to detector is achieved.

[030] Although the source collimator 225 is shown as a single, integrally formed body that has fins 226, conical surface 228, it need not be and could be formed of separate structural components, such as a source collimator combined with a detector collimator 248, while shielding as described in this document is achieved.

[031] In the illustrated embodiment, the housing region 230 around the opening in the source collimator and detectors 240 can be manufactured from beryllium, aluminum, titanium, or other metal or material with a low atomic number, the purpose is to allow more gamma rays enter the 240 detectors. This design is especially important for lower energy gamma rays, which are preferably absorbed by any dense metal in the pressure housing.

[032] Alternatively or in addition to the detector shield or collimator AO 248, an anti-coincidence algorithm can be implemented in electronic components 260 to compensate for the radiation dispersion of

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17/32 detector to detector. In this way, a processor can alleviate the effects of multiple gamma rays detected using an anti-coincidence algorithm. In certain embodiments, electronic components 260, 262, and 264 are located above detectors 240 or below source 220.

[033] Electronic components 260 may include processor 262, memory 263, and power supply 264 to supply power to the gravel fill imaging tool 200. Power supply 264 may be a battery or may receive power from an external source such as wiring (not shown). Processor 262 is adapted to receive the measured data from radiation detectors 240. The measured data, which in certain embodiments includes counting rates, can then be stored in memory 263 or further processed before being stored in memory 263. The 262 processor can also control the gain of the photomultiplier or other device to convert flicker into electrical pulses. Electronic components 260 can be located below source 220 and above or removed from detectors 240.

[034] In one embodiment, the tool additionally includes an accelerometer, an inclinometer with a geometric axis 3 or an attitude sensor to unambiguously determine the position of an azimuth segment. In certain embodiments, a compass device can be incorporated to further determine the orientation of the tool.

[035] The gravel filling imaging tool 200 can be constructed from any material suitable for the downhole environment in which it is expected to be exposed, taking into account in particular the temperatures, pressures, forces, and expected chemicals to which the tool will be exposed. In certain embodiments, the building materials suitable for the source collimator

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225 and detector collimator 248 include, but are not limited to, heavy metal, lead, materials with a very high and dense atomic number (Z), or any combination thereof.

[036] Furthermore, although a configuration tool with a diameter of 11 11/16 inches is illustrated, tool 100 can be sized as desired for a particular application. Those skilled in the art will appreciate that the larger diameter tool would allow for more detectors and shielding to provide additional segmentation of the gravel filling view.

[037] This tool can be arranged to measure the integrity of the gravel filling in new installations and to diagnose damage to the gravel filling from continuous production from the well. A person of ordinary skill in the art with the benefit of the present presentation will appreciate how to relate the results of the profile of the counting rates and the deducted densities of the gravel filling material to the fill structures and to consider from the results to a filling condition .

[038] As an additional illustration of an exemplary geometry of the embodiment illustrated in Figure 2, Figures 3A and 3B show cross-sectional views of another embodiment of the tool arranged in the base pipe or on the screen 330, which is additionally arranged in compartment 310 , which is additionally arranged in the filling with gravel 350, in which Figure 3A shows a cross section taken from the XY plane and in which Figure 3B shows a cross section taken from the XZ plane. As shown in the illustrated embodiment, the source collimator 328 is conically shaped in the X-Z or Y-Z plane. The detector 340 is shown in Figure 3A in openings or slots 345, where the radiation source 320 is shown illustrated in Figure 3B. As shown in Figure

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3A, detector collimators 348 are fan-shaped in the XY plane and rectangular in the X-Z or Y-Z planes. In certain embodiments, a tapered collimator source 328 is desirable since it reduces multiple dispersion events in the gravel filling.

[039] Methods for using the present invention may include the use of different energy windows to discriminate gravel filling in low to high density finishing fluids. In certain embodiments, at least three energy windows are used, each window depending on the energy of the source. For example, for a Cs (662 keV) source, the low-energy (LE) window (typically from about 50 keV to about 200 keV) is sensitive to multiple source scattered gamma rays, the window with high energy (HE) (typically from about 200 keV to about 350 keV) is sensitive to uniquely dispersed source gamma rays. A wide window (BW) can typically include gamma rays in the range of about 50 keV to about 350 keV. The BW count rate has the highest statistical accuracy and is used for base gravel filling imaging. The LE and HE windows can be used for specific applications, such as in-depth reading and maximum dynamic range imaging capabilities. The combinations of these different energy window profiles can be combined through the use of special methods (for example, ad-hoc adaptive or Kalman-type processing algorithms) for improved accuracy and resolution. It is recognized that energy sources with multiple intensity can be used in the same tool, either simultaneously or sequentially.

[040] In addition to the energy levels of the radiation source, other factors that can be adjusted to discriminate segmented views of the gravel filling include, but are not limited to, the collimator angle and the source for the detector for spacing. Examples of

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Suitable angles of the source collimator include, but are not limited to, angles of about 15 degrees to about 85 degrees and from about 65 degrees to about 85 degrees in other embodiments. Examples of suitable source of spacing for the detector include, but are not limited to, from about 2.54 cm (1 inch) to about 8.89 cm (3.5 inches) to about 20.32 cm (8) inches), and in other embodiments, from about 15.24 cm (6 inches) to about 25.4 cm (10 inches), and in still other embodiments about 30.48 cm (12 inches).

[041] Radioactive trackers can be used in conjunction with certain achievements to produce improved images of gravel filling. The introduction of radioactive trackers allows the production of an image of the material distributed in an azimuth way as a radioactive tracker. Radioactive trackers can be attached to the gravel filling before building the gravel filling or as the gravel filling is arranged. Alternatively, radioactive scanners can be injected or otherwise introduced into the gravel filling after installation of the gravel filling (for example, as a fluid or as a paste). More generally, radioactive scanners can be introduced into any portion of the formation, such as the well.

[042] When the radioactive tracker material is attached to the gravel itself prior to disposal, vacuum areas appear in the images as regions with a low (or “dark”) count, where the radioactive tracker material is injected as fluid or as a paste, the vacuum areas of vacuum areas appear in the images as regions with a high (or “clear”) count inside the gravel filling. Further image enhancement can be achieved by using a variety of trackers to create a multiple isotope profile.

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When used for this purpose, font 320 in Figure 3, 220 in Figure 2, or 120 in Figure 1 can be omitted from the tool. Alternatively, the radioactivity of the tracker can be determined in the presence of the radiation source or multiple trackers can be identified using the energy discriminating ability of electronic components 260.

[043] Furthermore, it is recognized that the downhole tool is capable of measuring counting rates although it is lowered or raised in the bore. In certain embodiments, the downhole tool can perform measurements even though the tool is immobile in the hole. Exemplary lowering elevation rates include displacement rates of up to approximately 54,864.000000001 centimeters / hour (1800 feet / hour).

[044] To facilitate a better understanding of the present invention, the following examples of certain aspects of some embodiments are provided. In no way should the following examples be read to limit, or define, the scope of the invention.

Examples

[045] In a non-limiting example of use, Figure 4 illustrates a graph of a spectrum of gamma rays incident on one of the detectors as a response to being dispersed in a filling with gravel. In this, the typical gamma ray intensity is shown plotted versus the gamma ray energy (MeV). This graph shows a simulation of detector energy spectrum modeled by MCNP of a real tool that results from the 356 keV 133Ba Compton gamma ray dispersed back in various gravel filling scenarios. This graph means an advantage to choosing a low power gamma source. By using an energy source that is low enough, it can be ensured that the gravel filling tool is particularly sensitive to variations in regions close to the gravel filling and is not significantly affected by dispersion

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22/32 in deeper regions of the cement around the compartment or formation and the subsequent variations in formation density. However, in the case of thick base pipes and metal screens between gravel filling and gravel filling tool detectors, the source energy needs to be high enough to penetrate into the gravel filling screen. In this way, gravel fill imaging tools can be designed to focus on particular depths or portions of a gravel fill.

[046] In a non-limiting example of use, Figure 5 shows a graph of a counting rate versus depth in centimeters as measured by an 8.89 cm (3.5 inch) gravel fill imaging tool. a 17.78 cm (7 inch) gravel filling. These profiles were produced by processing gamma ray count rates for individual detectors. The plot in Figure 5 is an MCNP modeled example of the count rate sensitivity for a 2.54 cm (1 inch) annular space undermining in a centered gravel filling at a depth index of 4 centimeters. It shows significant sensitivity to changes in gravel filling density. Qualitative image profiles will be produced by displaying the counting rates for each detector sector at each depth. Another means of analyzing the count can be used to compute a more quantitative multi-sector density profile (that is, in grams / cc). Such a density profile can be derived from the counting rates using a counting rate algorithm for calibrated profiling density.

[047] Notably, the traditional prior art density tool used to measure gravel filling generally has a relatively large spacing between the source and the detector. The reason for

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23/32 this is that the tool is provided to evaluate the entire filling with gravel. The source and the detector are both typically located centrally in the tool along the geometric axis of the tool. Shielding can be provided along the geometric axis between the source and the detector to prevent energy coupling between the two, that is, energy that passes directly from the source to the detector without dispersion within the gravel filling. In the prior art, because of the relatively large spacing between the source and the detector, gamma ray radiation undergoes significant multiple dispersion and absorption before it is detected and counted. The denser the filling with gravel, the lower the recorded count. In other words, in the prior art tools, the counting rate decreases with the gravel filling density due to the fact that multiple dispersion and absorption attenuates the total amount of radiation measured by the detectors.

[048] In an exemplary embodiment of the device and method of the present presentation, the source and the detectors are positioned in close proximity to each other, such as about 8.89 cm (3.5 inches) apart. Because of this close physical relationship, the energy propagated into the gravel fill and dispersed back to the detector goes through much less diffusion, that is, typically just a single diffusion (back to the detector) in a way opposite to dispersion multiple. In fact, the counting rates increase with the density of the gravel filling using the tool of the invention. This is significant because it means that the radiation does not pass through the attenuation associated with the prior art tools.

[049] Furthermore, the prior art does not use a conically shaped collimator to direct the propagated energy into the interior of the gravel filling. Again, through the use of such

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24/32 collimator in the prior art tool, multiple dispersion can be minimized and improved by imaging the prior art tools.

[050] Referring now to Figure 6, a partial side sectional view is provided to illustrate an exemplary embodiment of the tool 400 arranged in a hole 402 that crosses a formation 404. The tool 400 is suspended on a wire 406, which can be threaded through a wellhead assembly 408 shown established on the surface and in the opening for hole 402. Optionally, tool 400 could be arranged in the pipe, piano string, cable, or any later known or developed disposition medium. An external compartment 410 that can be cemented in the formation 404 outlines the hole 402 and an internal compartment 412 is shown inserted coaxially inside the external compartment 410. The tool 400 is suspended inside the production pipe 414 that inserts inside the compartment internal 412; a decentralizer 416 shown mounted on the side of tool 400 to propel tool 400 upward against the inner surface of production pipe 414. In one example, and as described in more detail below, decentralizing tool 400 improves space imaging between the concentric tubes.

[051] Referring now to Figure 7, shown in greater detail is a side sectional view of a portion of the Figure 6 embodiment. Fluid 418 is shown in the example of Figure 7 in production pipe 414. Fluid 418 also occupies the highest length of an annular space 420 between the internal and external columns of compartment 410, 412 and a portion of an annular space 422 between the internal compartment 412 and the production pipe 414. Below the fluid 418 and the annular space 422 exists a substantially solid precipitate 424 that extends between the pipeline

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25/32

414 and inner compartment 412. In the example in Figure 7, precipitate 424 adheres to tubing 414 to inner compartment 412. In one example, precipitate 424, which may fall or precipitate from fluid 418, can be substantially manufactured from baritin.

[052] Figure 8A is a sectional view of tool 400 in hole 402 taken along lines 8A-8A of Figure 7. In the example of Figure 8A, production piping 414 is substantially concentric within the inner compartment 412. Thus , in the example of Figure 8A the thickness Ar is substantially the same around the entire circumference of the annular space 422. Also shown in Figure 8A are detectors 4261-6 which are provided inside the tool body 400. In the example in Figure 8A, tool 400 is positioned against the inner surface of tubing 414 so that detector 4261 is the detector closest to the side wall of tubing 414. In contrast, detector 4264, which is illustrated to be about 180 ° at from detector 4261, it is the furthest detector from the side wall of tubing 414 against which tool 400 is propelled against.

[053] Referring now to Figure 8B, the partial sectional side view of the embodiment of Figure 8A is shown taken along lines 8B8B and illustrates a spatial relationship of detectors 4261, 4264 and a radiation source 428. In the example in Figure 8B and as described above, radiation source 428 emits radiation that is directed along dedicated paths to improve detection of scattered gamma rays. Still referring to Figure 8B, the trajectories P1, P4 are shown and illustrate an exemplary direction of radiation directed to detection by detectors 4261, 4264 respectively. By means of the asymmetric arrangement of tool 400 inside the pipe 414, the radiation directed along path P1 it leaves tool 400 and passes through piping 414 and into annular space 422. At least part

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26/32 of radiation along P1 that travels its way into annular space 422 disperses back and is detected by detector 4261. As will be described in more detail below, analyzing the radiation detected from detector 4261 can provide information on the material disposed within the annular space 422. In contrast, the radiation directed along the path P4 travels from the tool 400 and is directed into the fluid 418 inside the pipe 414. The strategic location of the source 428 and detector 4264 provides detection of radiation that mainly disperses from fluid 418. Thus, in an exemplary embodiment, a study of dispersed radiation monitored by detector 4264 can provide a reference or basis for analyzing the scattered gamma rays detected by the detector 4261.

[054] Figure 9A, like Figure 8A, is a sectional view of an example of tool 400 arranged in hole 402 taken sideways to the geometric axis AX of hole 402 (Figure 8B). In the example of Figure 9A, the tubing 414 is arranged asymmetrically within the inner compartment 412 so that the thickness Ar1 of the adjacent annular space 422 in which the tool 400 is located is smaller than other azimuth portions of the annular space 422. The asymmetric positioning of tubing 414 is shown in a longitudinal sectional view in Figure 9B, along with its representative directional trajectories P1, P4 that illustrate exemplary directions of the radiation that is emitted from the source 428.

[055] Referring now to Figure 10, a simulated count rate as recorded by detectors 4261, 4264 is provided graphically. More specifically, curves C1, C2 respectively illustrate situations in which the counting rates obtained by detectors 4261, 4264 can vary with changes in the thickness of the annular space 418. Curve C1 illustrates a simulated response in which a liquid is

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27/32 present in the annular space 422. The abscissa of Figure 10 represents a change in the thickness of the annular space, where the ordinate represents a ratio of the counting rate of detector 4261 to the counting rate of detector 4264. As shown, the ratio of the counting rates of detectors 4261, 4264 decreases with the decrease in the thickness of the annular space 422. The decrease in the counting rates can be attributed to more radiation that passes entirely through the annular space with a smaller width 422 and in contact with the surface internal of the internal compartment 412. The higher density of the material that composes the compartment 412 over the density of the liquid that can attenuate the radiation so that the dispersion cannot be observed at the level of energy that is detected by the detector 4261.

[056] The C2 curve of Figure 10 represents a simulated example in which the annular space 422 is substantially filled with a particulate matter such as baritin. In this example, the response ratio remains consistent enough despite changes in the thickness of the annular space 422. A plausible conclusion is that the rate of dispersion of the baritin radiation is substantially the same as that of another material that makes up the internal compartment 412. Equipped with this knowledge, the tool 400 can be successfully arranged inside the concentric tubes and used to determine the material inside the annular space for separating the tubes. In addition, changes in the coaxial orientation of the tubes should not affect the tool's ability to identify material within the annular space.

[057] Figure 11 illustrates a series of C3-C15 plots representing a counting response detected by a scattered radiation detector within various materials that have different densities. More specifically, the material density represented by the C3 plot is

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28/32 about 1.1982642681 grams per ml (10 pounds per gallon), the density of the material represented by each successive line increases by about 0.23965285362 grams per ml (two pounds per gallon). Thus, the density of the material represented by plot C4 is about 1.43791712172 grams per ml (12 pounds per gallon) and so on with the density of the material represented by plot C14 to be at about 3.83444565792 grams per ml (32 pounds per gallon). The C15 line represents baritin. In this example, the abscissa represents the thickness of the annular space and the ordinate represents the detected response. As can be seen from Figure 11, the response remains more consistent with changes in the thickness of the annular space for substances with higher density as opposed to those with lower density. As in the case of the response in Figure 10, the reduced thickness of the annular space allows the radiation to contact the internal surface of the compartment, which thus attenuates the radiation. A Monte Carlo modeling code MCMP was used as the modeling software that produced the data from which Figure 11 was generated.

[058] Referring now to Figure 12A, an example of a tool 400A that images a hole 402A is shown in a partial sectional side view. In this example a centralizer 430 is provided in a body 431 of tool 400A and holds tool 400A close to the middle portion of hole 402A. A portion of hole 402A adjacent to tool 400A is shown and is filled with gravel 432 which is composed of several pellets 434, such as a support material. Part of the gravel fill 432 is disposed in the annular space 420 and another part extends radially outwardly into the surrounding formation 404A through perforations 436 in compartment 437 shown as outlining hole 402A. In the example of Figures 12A and 12B a single column of the compartment

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29/32 is in hole 402A. In an alternative embodiment, the portion of compartment 437 that has perforations 436 can be a sleeve coupled to the remaining column of compartment 437. In addition, a screen (not shown) can be incorporated into the production pipeline 414 to filter sand and others particles that may enter the production pipe 414. As described in more detail above, the filling with gravel 432 can be imaged by means of radiation directed from source 428 along the Pi-Pn paths, in which the dispersion of radiation is detected with detector 426. Although a single detector 426 is illustrated in the embodiment of Figure 12A, multiple detectors 426 can be included. In an example of use, imaging of gravel fill 432 obtained by tool 400A, includes other portions of bore 402A or formation 404A, can provide an image of baseline fill with gravel 432.

[059] In one example, the baseline image can be obtained before any fluid production through filling with 432 gravel has occurred. Referring now to Figure 12B, the partial side sectional view of an example of how fluid flows over a period of time through filling with gravel 432B from formation 404B can introduce an amount of debris 438 into the filling with 432B gravel. In one example, detritus 438 includes fine particles or other solids that occupy the interstices between pellets 434B that make up the filling with gravel 432B which thus restricts the flow of fluid from the formation 404B through the filling with gravel 432B and for the inside of hole 402B. By placing the 400A tool inside the hole 402B and directing the radiation from the source 428 along the Pi-Pn paths and to the detector 426, as shown in Figure 12B, an image of the detritus 438 in the filling with 432B gravel can be obtained. Thus, the presence of detritus 438 can be identified or confirmed

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30/32 by comparing a baseline image of the 432 gravel filling with the image obtained subsequently.

[060] In one example, the baseline image can be obtained before repairing or repairing the 432 gravel fill, where a repair / repair example is an acidification procedure. Referring now to Figure 12C, hole 402C is imaged with tool 400A after operations to repair or repair the 432C gravel filling have occurred. In the example in Figure 12C, the gravel fill 432C continues to contain debris 438C that was not removed during the repair attempt. Then, by imaging the filler with gravel 432C with the tool 400A as shown, radiation from the source 428 disperses inside the filler with gravel 438C and detected by detector 426. Thus, the analysis of the detected diffusion can reveal the presence of and a location of the remaining 438C debris. Imaging the 402C hole with the 400A tool after a repair or repair of the 432C gravel filler can verify the repair procedure was successful, and if not, it can reveal how deep and azimuth debris 438C remains in the 432C gravel filler. Based on this information, decisions for future or additional repairs / repairs can be made.

[061] In Figure 13, the side sectional view of an exemplary embodiment of 400A is shown arranged in a hole 402 in which different types of and / or density of cement weight are arranged between compartment 437 and the surrounding formation 404. More specifically, a portion of the cement bond is composed of a lightweight cement 440 shown disposed in the annular space 420. In one example, the lightweight cement describes the cement between a compartment and a formation that has a density of up to about 1.43791712172 grams / ml (12 pounds / gallon). Also shown in the example in Figure 13 is a cement with normal weight

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442 disposed in the annular space 420 above the light weight cement 440. For the purposes of the discussion in this document, the normal weight cement may include cement between a compartment and a formation that has a density greater than about 1.43791712172 grams / ml (12 pounds / gallon). The tool 400A of Figure 13 is configured so that the radiation from its source 428 is directed along the paths Pi-Pn and that the dispersion of radiation that occurs inside the annular space 420 that has cement 440, 442 is detected by the detector 426. Because of the sensitivity and resolution of the 400A tool, radiation will disperse from light weight cement 440 different from how it will disperse from cement with normal weight 442. Furthermore, an analysis of the differences in detecting detector 426 when tool 400A is disposed adjacent to different cements 440, 442, it can identify the specific locations of those different cements 440, 442.

[062] Referring now to Figure 14, an example of tool 400A is illustrated in a partial side sectional view arranged in a hole 402 in which asphaltenes 444 are produced from formation 404. In this example, asphaltenes 444 can be become housed in the filling with gravel 432 in the well as perforation 436 takes place in compartment 437. Similar to the example of the operation in Figure 13, the radiation from source 428 in tool 400A is directed out radially from tool 400A of so that a part of the radiation is dispersed from the asphaltenes 444 in the filling with gravel 432 or on the screen 436. Detecting the radiation diffusion with the detector 426 and the analysis of the detection results can indicate the presence and / or the location of the asphaltenes 444 when filling with gravel 432 or on screen 436. In one example, the presence of asphaltenes is detected by detecting the energy level (s) of the radiation detected with detector 426 to be consistent with the level (s) of

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32/32 radiation energy known to diffuse from asphaltenes 444.

[063] In Figure 15, an exemplary embodiment of the tool 400A is shown in a partial sectional side view. In this example, tool 400A is equipped with a centralizer 430 that positions tool 400A towards the middle portion of hole 402. The radiation is directed from source 428 along the Pi -Pn paths so that the radiation that disperses at from the annular space 420 it can be detected by the receiver (s) 426. In one example, strategically forming collimator 328 (Figure 3B) and spatially locating the source 428 and the detector (s) 426 allows detecting the radiation diffusion desired by the detector (s) 426. Also optionally, monitoring the dispersion in a range of selective energy can indicate the material disposed in the annular space 420. In the example of Figure 15, precipitate 424 is detected in the annular space 420 upon analysis the scattered radiation count detected by the sensor (s) 426, in which the precipitate 424 may include baritin.

[064] The present invention described in the present document, therefore, is well adapted to carry out the objectives and achieves the mentioned purposes and advantages, as well as others inherent to it. Although a currently preferred embodiment of the invention has been provided for the purposes of presentation, numerous changes exist in the details of the procedures to achieve the desired results. Such and other similar modifications will readily arise on their own to those skilled in the art and are intended to be encompassed within the spirit of the present invention presented in the present document and within the scope of the appended claims.

Claims (20)

1. METHOD FOR DETERMINING AN UNDERGROUND Borehole (402), comprising: (a) directing a first set of radiation from inside a tube (412) disposed in the underground hole (402) and along a first oblique path to a geometric axis of the tube (412), so that at least part of the radiation passes through the tube (412) into an annular space (422) that circumscribes the tube (412) and disperses back into the tube (412); (b) detecting radiation that disperses back into the tube (412); and characterized by (c) identifying a material in the annular space (422) based on a detection rate of the first radiation set; directing a second set of radiation along a second path that has an azimuthal component that is 180 ° from an azimuthal component of the first path so that at least part of the second set of radiation is dispersed from the fluid disposed in the tube (412) and detecting the second set of scattered radiation; wherein the step of identifying a material in the annular space (422) is additionally based on a detection rate of the second set of radiation. 2. METHOD according to claim 1, characterized in that the radiation comprises a gamma ray from a source of gamma ray (428) which has an energy of 250 keV to 700 keV and in which the scattered radiation, when detected, has an energy of 50 keV to 350 keV. 3. METHOD according to any one of claims 1 to 2, characterized by the repetition of steps (a) to (c) in a Petition 870200000568, of 03/01/2020, p. 44/93 2/7 different depth in the hole (402) and where a thickness of the annular space (422) varies around a circumference of the annular space (422) so that a detectable amount of energy from at least part of the radiation is attenuated inside an external tube (437) that circumscribes the annular space (422). 4. METHOD, according to any of the claims 1 to 2, additionally characterized by: repeat steps (a) to (c) at a different depth in the hole where the annular space (422) has a thickness that varies along a circumference of the annular space (422) so that a detectable amount of energy from the at least a part of the radiation is attenuated inside an external tube (437) that circumscribes the annular space (422), and detects a fluid in the annular space (422) when a ratio of the detection rate of the first set of radiation above the detection rate of the second set of radiation decreases when the thickness decreases. METHOD according to any one of claims 3 to 4, characterized by the detection of a solid material in the annular space (422) when a ratio of the detection rate of the first set of radiation to the detection rate of the second set of radiation remains the same with changes in thickness. METHOD, according to any one of claims 1 to 5, characterized in that the material in the annular space (422) comprises a lightweight cement. METHOD, according to any one of claims 1 to 6, characterized by the radiation being from a source (428) disposed in a downhole tool (200) disposed in the tube (412) and in a location selected from from a group consisting of asymmetrically against an inner surface of the tube (412) and a portion Petition 870200000568, of 03/01/2020, p. 45/93 3/7 median of the tube (412). METHOD according to any one of claims 1 to 7, characterized in that the tube (412) is an inner tube (412) and the annular space (422) is provided between the inner tube (412) and an outer tube (437 ) that are coaxially arranged in an underground hole (402), the method comprising: (d) provide a gamma ray source (428) arranged in a profiling instrument against an azimuthal section of the inner tube (412); (e) direct the gamma rays from the source (428) so that some of the gamma rays move through the side wall of the profiling instrument into the annular space (422) and diffuse from a material in the space annul (422) back into the inner tube (412) and so that some of the gamma rays move away from the azimuth section of the profiling instrument and diffuse from a fluid in the inner tube (412); (f) detecting the scattered gamma rays and classifying the gamma rays that disperse from the fluid in the inner tube (412) and those that disperse from the material in the annular space (422); and (g) identifying the material in the annular space (422) based on a detection rate of the scattered gamma rays. 9. METHOD according to claim 8, characterized in that a conically shaped guide is supplied close to the gamma ray source (428) and positioned on the profiling instrument so that an apex of the guide is directed towards the source (428) and the guide has a geometric axis that is parallel to a geometric axis of the inner tube (412). A method according to any one of claims 8 to 9, characterized in that a detector is arranged from 5.08 cm to 10.16 cm from the gamma ray source (428) and in which the detector is used to detect the Petition 870200000568, of 03/01/2020, p. 46/93 4/7 scattered gamma rays. 11. METHOD, according to any of the claims 8 to 10, characterized in that a collimator (225) is used to direct the gamma rays away from the source (428) at an angle oblique to a geometric axis of the inner tube (412) and along different paths arranged azimuthally to the around the gamma ray source (428), so that the detectors detect, respectively, the dispersion from the distinct azimuth areas radially spaced out from the gamma ray source (428). 12. METHOD, according to any of the claims 8 to 11, characterized by a rate of detection of gamma rays that deviate from the fluid in the bore is used as a reference to determine the material in the annular space (422). 13. METHOD according to any one of claims 8 to 12, characterized by the repetition of steps from (d) to (g) at different depths in a section of the bore and identifying a solid material in the annular space (422) when a ratio of a rate of detected gamma rays that are dispersed from the annular space (422) above a rate of detected gamma rays that are dispersed from the fluid in the inner tube (412) remains the same with changes in the thickness of the annular space ( 422). 14. METHOD, according to any of the claims 8 to 13, characterized by the repetition of steps (d) to (g) at different depths in a section of the bore and the identification of a liquid material in the annular space (422) when a ratio of a rate of detected gamma rays that are dispersed from the annular space (422) above a rate of detected gamma rays that are dispersed from the fluid in the inner tube (412) is reduced with a reduction in the thickness of the annular space (422). 15. METHOD, according to any of the claims Petition 870200000568, of 03/01/2020, p. 47/93 5/7 1 to 7, characterized in that the tube (412) is an inner tube (412) and the annular space (422) is provided between the inner tube (412) and an outer tube (437) which are coaxially arranged in an underground hole (402), the method comprising: (h) provide a gamma ray source (428) arranged in a profiling instrument against an azimuthal section of the inner tube (412); (i) directing the gamma rays from the source (428) so that some of the gamma rays move into the annular space (422) and diffuse from a material in the annular space (422) back to the interior of the inner tube (412) and so that some of the gamma rays move away from the azimuth section and disperse from a fluid in the inner tube (412); (j) detecting the scattered gamma rays and classifying the gamma rays that disperse from the fluid in the inner tube (412) and those that disperse from the material in the annular space (422); (k) identifying the material in the annular space (422) based on a detection rate of the scattered gamma rays; and (l) repeat the steps from (h) to (k) at different depths in a section of the hole, identifying a solid material in the annular space (422) when a ratio of a rate of detected gamma rays that are dispersed from the annular space (422) above a rate of detected gamma rays that are dispersed from the fluid in the inner tube (412) remains the same with changes in the thickness of the annular space (422), and identify a liquid material in the annular space (422 ) when a ratio of a rate of detected gamma rays that are dispersed from the annular space (422) above a rate of detected gamma rays that are dispersed from the fluid in the inner tube (412) is reduced with a reduction Petition 870200000568, of 03/01/2020, p. 48/93 6/7 in the thickness of the annular space (422). 16. METHOD, according to claim 15, characterized by the repetition of step (l) along the sections of the hole (402) that are at different depths. 17. METHOD according to any one of claims 15 to 16, characterized in that the rate of gamma rays that are dispersed from the fluid in the tube (412) comprises a reference value for use in the identification of a liquid in the annular space ( 422). 18. METHOD, according to any one of claims 1 to 17, characterized by comprising: forming a baseline image of the gravel filling (432) by directing the radiation into the gravel filling (432) and detecting the dispersion of radiation from the gravel filling (432); at a point in time after forming the baseline image, form an updated image of the gravel fill (432) by directing the radiation into the gravel fill (432) and detect radiation dispersion from the fill with gravel (432); compare the baseline image and the updated image; and identifying a material that has migrated into the gravel fill (432) in a period of time between when the baseline and updated images are formed. 19. METHOD according to claim 18, characterized in that the material is selected from a group consisting of detritus (438) from a formation adjacent to the filling with gravel (432) and asphaltenes (444). 20. METHOD, according to claim 18, characterized by the formation of an image of the filling with gravel after repair Petition 870200000568, of 03/01/2020, p. 49/93 7/7 (432) by directing radiation into the gravel filling (432) and detecting radiation dispersion from the gravel filling (432) at a point in time after forming the baseline image and after the gravel filling (432) has been repaired.